Horizontal coreless induction furnaces

ABSTRACT

There is disclosed herein a horizontal coreless induction furnace having a polyphase coil that is electrically energized to establish a unidirectional stirring motion within the horizontally disposed corelss melt section of the furnace to prevent or reduce the build up of nonmetallics within the power coil surrounded portion of the furnace.

United States Patent Duca [451 May28, 1974 HORIZONTAL CORELESS INDUCTION FURNACES [75] Inventor: William J. Duca, Warren, Ohio [73] Assignee: Ajax Magnethermic Corporation,

Warren, Ohio [22] Filed: Apr. 30, 1973 [2i] Appl. No.: 355,647

[52] US. Cl. 13/29 [51] Int. Cl F27d 11/06, HOSb 5/14 [58] Field of Search 13/29, 26

[56] References Cited UNITED STATES PATENTS 1,81 L644 6/1931 Northrup r. 13/29 3,483,301 l2/l969 Duca l3/29X Primary Examiner-Roy N. Envall, Jr.

[57] ABSTRACT There is disclosed herein a horizontal coreless induction furnace having a polyphase coil that is electrically energized to establish a unidirectional stirring motion within the horizontally disposed corelss melt section of the furnace to prevent or reduce the build up of nonmetallics within the power coil surrounded portion of the furnace.

4 Claims, 4 Drawing Figures HORIZONTAL CORELESS INDUCTION FURNACES This invention relates to the induction heating and melting of metal and particularly to a means of applying power to a horizontal coreless induction furnace. This invention relates to improvements in horizontal coreless induction furnaces of the type set forth, described and claimed in US. letters Pat. Nos. 3,483,301 patented Dec. 9, 1969 and 3,602,625 patented Aug. 31, 1971.

In the horizontal coreless induction furnaces disclosed in the aforementioned patents, a single phase induction heating coil is wound annularly about a horizontal melting tunnel of the furnace. Energization of the induction coil establishes circumferential secondary currents within the molten metal and also causes a pattern of circulation within the molten metal shown by closed loops in the drawings herein which loops are termed quadrantal" herein.

The aforesaid molten metal circulation can transport nonmetallic particles such as molding sand or iron oxide which become dispersed in the molten iron as the charge melts. It has been found that such nonmetallic particles are transported into the heating coil region of the furnace and that, due to the opposing stirring forces within the single phase quadrantal stirring pattern, they will be entrapped near the center of the heating coil on the refractory surfaces of the horizontal melting tunnel.

The horizontal coreless induction furnace of the present invention is constructed to achieve unidirectional stirring of the molten metal within the horizontal tunnel of the furnace as contrasted to the prior quadrantal stirring referred to and thereby prevent the buildup of nonmetallic particles within the power coil region.

It is hence an object of this invention to provide means for preventing the entrapment of metal oxides and/or gases within the melt section.

Another object of this invention is to prevent or reduce the formation of slags by interaction between nonmetallic particles at the power coil surrounded refractory surface or wall of the so-called horizontal coreless induction furnace.

Another object of this invention is to prevent attack of the power coil surrounded refractory walls by slags formed as a result of interaction between nonmetallic particles deposited thereon.

A further object of this invention is to provide means whereby the unidirectional flow of molten metal in a horizontal coreless furnace may be selectively achieved in either direction as desired.

Other objects of this invention and the invention itself will become more readily apparent from a purview of the following description, referred to in the appended drawings. in which drawings:

FIG. I is a longitudinal section through a furnace of the type referred to showing the stirring pattern for a single phase coil as shown in the cited prior art;

FIG. 2 is a longitudinal section through the furnace of this invention showing the stirring pattern for a polyphase coil according to the invention wherein the direction of the molten metal circulation may also be reversed from that shown;

FIG. 3 is an electrical diagram showing one type of polyphase power system connection to the coil in the furnace of this invention; and

FIG. 4 is a voltage, current and flux vector diagram for the polyphase coil in the furnace of this invention.

Referring now to the drawings, in all of which like parts are designated by like reference characters, 10 indicates generally the horizontally disposed coreless induction furnace of this invention. It may be suitably adapted for melting or superheating any metal or alloy, but is expected to be particularly useful in ferrous metallurgy. Furnaces of this type are used commonly for melting metals, and the usual procedure is first heating molten metal inductively in the heating section of the furnace, the heated molten metal in turn melting the cold metal introduced through the charging section. In FIG. I, the molten metal 15 is shown contained within the refractory lining 19 of the horizontally disposed heating section 16, substantially vertically disposed charging section 17, and substantially vertically disposed pour section 18. Cooling coil sections 22, 24, are shown disposed coaxial with the heating and stirring coils 20 at either end thereof and said coil sections are not supplied with current. The induction heating and stirring power coil 20 is cylindrically wound about the horizontal portion 16 of the furnace which constitutes the principal metal containing cavity of the furnace.

Should the coil 20 be connected as a single phase load, a stirring pattern 25 as shown in FIG. 1 occurs. This is commonly referred to as quadrantal stirring. It has been found that if any nonmetallic material, such as finely dispersed metal oxides or gas bubbles resulting from the reduction of these metal oxides, is caught in the horizontal movement of the metal, it would be transported to a location adjacent the center of the coil and remain in such location by entrapment due to the opposing stirring forces and the fact that nonmetallic materials are not acted upon electromagnetically. As a result metal oxide buildup and/or the formation of a pocket of gas 26 tends to take place. This phenomena can occur even though the height of the metal in the charge section 17 and the pour section 18 is adequate to prevent surface slagfrom being drawn down into the heating section 16 as disclosed in US. letters Pat. No. 3,483,301.

lf nonmetallic particles of more than one kind are accumulated near the coil center, such as for instance silica and iron oxide, a low melting point slag may be formed. The refractory lining may also participate in such a slag-forming reaction.

The formation of either a slag or metal oxide buildup or a pocket of gas is undesirable within the power coil surrounding the horizontal melting portion of the furnace as metal is displaced thereby from the refractory lining causing a decrease in power for a given applied voltage. This loss of power can seriously affect the melt rate capability of the furnace. The case of a gas pocket is not as serious as a slag or metal oxide buildup since it represents only a temporary loss in melt rate. Gas will escape from the furnace when the power is shutoff and there is no force to maintain a gas pocket. A slag or metal oxide buildup on the other hand cannot be easily disposed of and will result in a permanent reduction in the melt rate unless it is removed.

Furthermore, if interaction between nonmetallic particles results in the formation of a low melting point slag and if the refractory lining participates in this reaction serious deterioration of said lining can occur.

It is proposed in the present invention that the coil 20A be connected as a polyphase load, as for example from a three phase input from an alternating current source, in which case a stirring pattern as shown at 30 in FIG. 2 occurs. This will be referred to herein as unidirectional stirring. The stirring pattern, it is to be noted, in this form extends beyond the power coil section refractory surfaces. If any nonmetallic material such as finely dispersed metal oxides or gas bubbles resulting from the reduction of metal oxides are caught in the horizontal movement of the metal, the same will be transported through the horizontal heating section 16 by virtue of the unidirectional stirring achieved and buildup, slag formation, or gas pockets are prevented.

ln FIG. 3, the coil 20 of the horizontal coreless furnace of this invention is shown as a three-section power coil with one center section 36 of the power coil reverse wound from the outer sections 35 and 37. The coil is connected to a three-phase supply L1, L2, L3 in such a manner that each phase-to-phase voltage ener: gizes one coil section. Capacitor banks-38, 39, and 40 are employed to correct the furnace power factor as is well known to those skilled in the art.

A simplified showing of electromagnetic aspects of the connection of FIG. 3 is illustrated by vector diagrams of voltage E, current I, and flux 1 in H0. 4.

It will be noted that by connecting the two coils 35 and 37 on two phases of a three phase-system, and by reversing the winding of the center coil 36 connected to the third phase with respect to the other windings 35 and 37, the magnetic field characteristics D 12, d) 23 and 21 are 60 out of phase. Hence, the molten metal is transported unidirectionally along the power coil surrounded refractory walls in the direction of the traveling field as shown in H0. 2.

If desired, any two of the three-phase lines are reversed and the same type of action occurs except that the metal is transported unidirectionally in the opposite direction.

Although a preferred embodiment of this invention has been described, it will be obvious that other forms thereof will become apparent to one skilled in the art; however, the disclosure of the preferred embodiment is not intended to limit the scope of this invention beyond that recited in the following claims.

I claim:

1. A horizontal coreless induction furnace for heating or melting metal comprising a horizontally disposed heating chamber having two axially spaced openings therein, a reservoir angled with respect to and extending upwardly from said chamber and communicating with one opening in said chamber, a second reservoir angled with respect to and extending upwardly from said chamber and communicating with the other opening therein, one of said reservoirs being adapted to receive a charge of metal to be heated or melted and the other reservoir being adapted to discharge molten metal therefrom, and an induction power coil supplied with polyphase current, said coil wound about the horizontally disposed heating chamber, the axis thereof coinciding with the axis of the said chamber and providing heating and unidirectional stirring of the metal in said heating chamber through the length of the coil wherefore finely dispersed metal oxides and gas pockets are not entrapped therein.

2. A horizontal coreless induction furnace as in claim 1 wherein selective means are provided for causing said unidirectional stirring in an opposite direction.

3. A method for melting or heating metal in a coreless induction furnace having an open ended horizontally disposed heating chamber, two reservoirs each in communication with an end of said heating chamber, and an induction power coil comprising, introducing a charge of metal through one of said reservoirs, supplying polyphase current to said coil to heat said charge to a predetermined temperature to melt said charge and to unidirectionally stir said molten metal in said heating chamber and transport said molten metal throughout the length of the coil whereby metal oxides and gas pockets are not entrapped therein.

4. A method of heating metal as in claim 3 wherein the molten metal is discharged from the other reservolr. 

1. A horizontal coreless induction furnace for heating or melting metal comprising a horizontally disposed heating chamber having two axially spaced openings therein, a reservoir angled with respect to and extending upwardly from said chamber and communicating with one opening in said chamber, a second reservoir angled with respect to and extending upwardly from said chamber and communicating with the other opening therein, one of said reservoirs being adapted to receive a charge of metal to be heated or melted and the other reservoir being adapted to discharge molten metal therefrom, and an induction power coil supplied with polyphase current, said coil wound about the horizontally disposed heating chamber, the axis thereof coinciding with the axis of the said chamber and providing heating and unidirectional stirring of the metal in said heating chamber through the length of the coil wherefore finely dispersed metal oxides and gas pockets are not entrapped therein.
 2. A horizontal coreless induction furnace as in claim 1 wherein selective means are provided for causing said unidirectional stirring in an opposite direction.
 3. A method for melting or heating metal in a coreless induction furnace having an open ended horizontally disposed heating chamber, two reservoirs each in communication with an end of said heating chamber, and an induction power coil comprising, introducing a charge of metal through one of said reservoirs, supplying polyphase current to said coil to heat said charge to a predetermined temperature to melt said charge and to unidirectionally stir said molten metal in said heating chamber and transport said molten metal throughout the length of the coil whereby metal oxides and gas pockets are not entrapped therein.
 4. A method of heating metal as in claim 3 wherein the molten metal is discharged from the other reservoir. 